The present invention relates to a method for improving the traffic handling capacity of a packet switched mobile telephone communication system.
GPRS is a new standard for packet switched mobile telephony. This invention proposes an improvement in the SGSN for the NS ETSI specification, see ref. [1], of the GPRS interface, i.e. the interface from SGSN towards BSS (downlink direction).
Problem
On the Gb-interface, see FIG. 1, there are a number of links (NS-VCs) between the SGSN and the BSS. The number of links might vary from one to many hundreds. In the NS ETSI specification, see ref. [1], section 4.4.1, bullet two, it is stated that traffic related to a specific MS (LSP) should be transmitted on the same link (NS-VC). This will ensure in order delivery of packets from the SGSN to the BSS or vice-versa for one MS. Transmission capability of the different links might very well be different. The in-order delivery might be jeopardised if using multiple links for the same MS. Hence, if packet 1 is sent from the SGSN to the BSS on link 1, and then the next packet, packet 2, is sent on link 2, then we are not guaranteed that packet 1 will arrive before packet 2 at the BSS. According to ref. [1] section 4.4.1, bullet two, another link will be selected when the used link fails. In this link failure case it accepted to receive traffic out of order.
The specified Load sharing function in ETSI specification, ref. [1], section 4.4.1, covers the following use cases:
New LSP (MS) shall be allocated a NS-VC, and in order delivery of NS-SDU are preserved
Link failure, another link will be selected, traffic might be received out of order
Block/unblock of links (NS-VC), traffic shall be received in order
The use case: xe2x80x9cOne link is congestedxe2x80x9d is not specified for the Load Sharing function in ref. [1].
The problem with not being able to migrate traffic for an MS from one link to another, is that if the link currently assigned gets congested then there is no way of reducing the traffic load on the congested link. I.e. if the link gets congested the MS can not send on another link which is not congested instead, since that might inflict out of order delivery of the packets. The problem is: xe2x80x9cis it possible to migrate traffic (due to congestion) without inflicting in order delivery?xe2x80x9d
From U.S. Pat. No. 5,649,110, there is known a method for equalizing (by buffering) and give priority to traffic in a communication network.
U.S. Pat. No. 5,488,607 relates to a method for evaluating the throughput in a packet switched system (ATM). A similar method is also known from U.S. Pat. No. 5,132,961.
ETSI Spec. GSM 08.16 relates to load sharing in case of
New subscribers (LSP/MS)
A break in the channel
Blocking/de-blocking of channels
However, none of the publications mentions what should be done when a channel is congested.
Introduction
The problem described above are solved according to the invention by introducing a load sharing function between the BSS and the SGSN. The load sharing function is situated in the network service control sublayer, which is a sublayer of the network service layer. The purpose of the load sharing function is to distribute the traffic load from the SGSN to a BSS (downlink traffic) among the available NS-VCs.
Between the SGSN and a BSS, there will be one or more NS-VCs for each NSE. An NSEI identifies a group of NS-VCs. The responsibility of the load sharing function is to distribute the NS SDU traffic among the available NS-VCs of the same group.
A requirement for the load sharing function is that it should ensure that NS SDUs with the same LSP should be sent on the same NS-VC, this to ensure that for each BVC, the in order delivery of all NS SDUs marked with the same LSP value are preserved.
The load sharing function is only invoked in the SGSN for downlink traffic.
The scope of the present invention is as defined in the appended claims.